1. Field of Invention
The invention relates to a power control device and a method thereof and, in particular, to a power control device and a method thereof of single base power for an optical disk drive.
2. Related Art
An optical read/write module of an optical disk drive is easily affected by heat thus the performance and accurate of the electric device may be influenced. In order to control the electric device at different temperatures, a proper control module must be designed to modify the affection resulted from the thermal factor.
Referring to FIG. 1, an optical disk drive 1 includes an optical read/write module 11 and a power control module 12. The optical read/write module 11 includes a light-emitting unit 111, a light-sensing unit 112, and a plurality of current control units 113, 114 and 115. The light-sensing unit 112 detects the output power of the light-emitting unit 111 and generates a power feedback signal 112A. The power control module 12 determines whether the output power of the light-emitting unit 111 reaches a target value according to the power feedback signal 112A, and generates a power control signal 121 according to the determination. In addition, the current control units 113 to 115 modulate the currents 113A to 115A according to the power control signal 121, respectively. Therefore, after being driven by the currents 113A to 115A, the light-emitting unit 111 generates the output power reaching the target value.
Referring to FIG. 2, when the light-emitting unit 111 is at a temperature T1, the output power and the operating current of the light-emitting unit 111 are related in a line L1. In other words, when the operating temperature of the light-emitting unit 111 is at the temperature T1 and the operating current is at currents Ib, Ie, or Iw, the light-emitting unit 111 generates the output power at powers Pb, Pe or Pw.
In order to control the operating currents generated by the light-emitting unit 111 exactly at the different powers, the conventional power control module 12 controls the currents 113A, 114A and 115A respectively to be equal to the current Ib, the current Ie minus the current Ib, and the current Iw minus the current Ie. Besides, the light-emitting unit 111 can be driven by the different combinations of the currents 113A to 115A.
For example, if the power control module 12 controls the light-emitting unit 111 to generate the output power at the power Pe, the current control units 113 and 114 are enabled by the power control module 12. Therefore, the light-emitting unit 111 is driven only by the currents 113A (current Ib) and 114A (current Ie minus current Ib) to generate the output power at the power Pe.
On the other hand, if the temperature of the light-emitting unit 111 rises to a temperature T2, the power control module 12 increases the operating current of the light-emitting unit 111 (as dotted line A) with a closed feedback control method based on the power Pe according to the power feedback signal 112A until the output power of the light-emitting unit 111 reaches the power Pe.
However, the operating current of the light-emitting unit 111 is still equal to the current Ie, such that the light-emitting unit 111 generates the output power at the power Pe′. In order to adjust the output power of the light-emitting unit 111 to the power Pw, the power control module 12 computes the current Iw′ resulting in the power Pw according to the current Ie and the relationship between the power Pw and the power Pe′, as shown in formula 1.
                              I          w          ′                =                                                            P                w                                            P                e                                      ⁢                          (                                                I                  e                  ′                                -                                  I                  e                                            )                                +                      I            w                                              (        1        )            
In addition, A current Ib′ resulting in the power Pb is computed in the same computing method. Therefore, the power control module 12 can control the currents 113A, 114A and 115A respectively be equal to the current Ib′, the current Ie minus the Ib′, the current Iw′ minus the Ie. Accordingly, the light-emitting unit 111 is able to generate the output power at different powers (Pb, Pe, Pw) at the temperature T2. In brief, the conventional technology is to compute the operating-currents of the light-emitting unit 111 to generate the output power at different powers at the temperature T2 according to the line L2.
However, when the light-emitting unit 111 actually reaches the temperature T2, the output power and the operating current of the light-emitting unit 111 are not related in the line L2 but a line L3. Therefore, the operating current computed according to the conventional technology is the current Iw′, so that the light-emitting unit 111 generates the output power at power Pw′ (as dotted line B), which is not correctly controlled at power Pw. In the same manner, the light-emitting unit 111 does not generate the output power at power Pb (as dotted line C) correctly. The errors in the above cases are caused by that the conventional technology ignores the threshold-current It1 and It2 (intersection points of line L1 and line L3 with the current axis, repectively). As shown in FIG. 3, the temperature of the light-emitting unit 111 is in exponential relation to the threshold-current. If the threshold-current is insufficient, the operating-current computed by the conventional technology for obtaining the output power at different temperature would not have an obvious error. However, if the threshold-current is sufficient or the output power is to be precisely controlled, the error of the operating-current computed by the conventional technology is inevitable.
Referring to FIG. 4, the light-emitting unit 111 of the conventional optical read/write module 11 generates the output power Pout to access an optical disk. If the temperature of the light-emitting unit 111 changes (for example, increasing the temperature), the output power Pout is well controlled at the power Pe but not the power Pw and Pb due to the regardless of the threshold-current. Further, according to the increase of the temperature, the output power Pout lapses from the wrinting power Pw and Pb (the dotted line in FIG. 4).
Similarly, as shown in FIG. 5, according to the conventional method and multipulse write strategy, only the power Pb as the base power can be controlled correctly. And, the output power Pout lapses from the correct wrinting power Pw (the dotted line in FIG. 5). Therefore, the optical read/write module 11 does not correctly access the optical disk, and, even more, the lifetime of the optical read/write module 11 and the endurance of the optical disk drive 1 are reduced.
It is therefore a subject of the invention to provide an optical disk drive with a single power baseline control, which considers an effect of the threshold-current of the optical read/write module in the optical disk drive at different temperature, and computes the operating-current for driving the optical read/write module to generate the distinct output power according to a single power baseline. Thus, the output power of the optical read/write module can be precisely controlled.